What are the black squares on Seattle roadways? Gang signs?

One of the black squares in question. (Seattle Department of Transportation photo)

Q: I see these black squares in the middle of the road all over the place and no one seems to know what they are there for. Are they to monitor traffic? Are they some gang’s way of marking its territory?

I found four more on Trenton Avenue Southwest in West Seattle just east of the post office driveway the other day. Others are on Aurora Avenue North and Harbor Avenue Southwest.

Can you please ask the Seattle Department of Transportation folks if they know of anything?

A: The markings aren’t for a gang’s territory, unless you consider the National Highway Traffic Safety Administration a gang. But they’re even less threatening than the Jets.

“Your reader has spotted black tape squares that indicate someone has performed a traffic study at these locations using a portable traffic analyzer. We believe the markings were left by a study completed a short while ago by the National Highway Traffic Safety Administration.

“The national study monitored speeds on all classes of roadways ranging from highways to residential streets for research purposes.

“These analyzers were affixed to the roadway using an asphalt-based tape. The analyzer is cut from the tape once the study is finished, leaving a black tape square with an oval shape inside affixed to the roadway.

“It would be fairly difficult to remove the tape completely without more costly traffic controls as the tape is very sticky and a torch and scraping process would be required to strip the remaining residue from the roadway. That wouldn’t have been cost effective given that most of these locations are heavily traveled around-the-clock and the tape is eventually worn off by the traffic.